Determining the local state of polarization of a generally elliptically polarized light wave field demands for each point a time-consuming measuring of the intensity transmitted by an analyzer at various azimuth angles. Evaluating the measuring results to determine the so-called polarization ellipse defining the state of polarization at the respective point of the wave field is also complicated and in many cases only possible with a computer. A point-by-point examination of large light wave fields with polarized radiation is therefore exceptionally complex; on the other hand, for many measurings it is very useful to know this state of polarization.
One such case is the problem of determining the local characteristics of thin transparent layers over a substrate, e.g. insulation and passivation layers in the production of integrated circuits. To obtain the necessary circuit parameters the thickness of these layers is to be determined with great precision during or after their production. If the index of refraction of the layer is known, this can principally be effected with interferometric measuring methods. However, the indices of refraction of thin layers depend very much on their method of production so that their precision definition is impossible without actually measuring. For simultaneously determining layer thickness and index of refraction of a thin transparent layer, the ellipsometric method offers maximum precision. In this method, a polarized light beam of small diameter and oblique incidence is directed onto the layer to be examined, and the intensity of the reflected beam is determined as a function of the azimuth angle of an analyzer. The measured intensity distribution determines the state of polarization of the reflected beam in the form of a so-called polarization ellipse which in turn permits determination of thickness and index of refraction of the layer.
Such a point-by-point measuring technique requires a relatively large amount of time. This is true also for those cases where measuring is effected in so-called automatic ellipsometers where the analyzer rotates with a high speed. For time reasons, the point-by-point ellipsometric measuring of large surfaces is therefore possible in exceptional cases only. Furthermore, the spatial resolution of the measuring is low owing to the oblique incidence.
Light wave fields with locally different polarization state can also be employed for a number of further applications, provided a speedy and local evaluation of the state of polarization is possible. Examples are photo-elasticity, crystal optics, or saccharimetry.